Cell surface macromolecules will be isolated from differentiated mouse neuroblastoma cells by using metabolic turnover, chaotropic ion extraction, and detergent extraction. These preparations will be adsorbed with solid phase antisera to fetal calf serum and non-neural murine tissue culture cells. Then they will be assayed for biological activity by testing their ability to inhibit the finding of an iodinated rabbit anti-neuroblastoma serum. Active preparations will be incubated with fused rat myotubes in culture to test for specific binding of neural proteins to muscle cells. A variety of controls including binding of neural macromolecules to non-muscle monolayers and binding of non-neural macromolecules to myotube monolayers will be analyzed to insure that only specific nerve-muscle binding species are studied. The specifically bound macromolecules will be dissociated from the muscle surface and purified using rebinding to muscle monolayers as a purification assay. Purified macromolecules will be characterized by molecular weight and isoelectric point determination and also analysis of amino acid, carbohydrate and lipid composition. The topographic pattern of specific binding will be compared to the cell surface distribution of the acetylcholine receptor and also the position of the muscle nuclei. Parallel studies using primary cultures of nerve and muscle will also be carried out. Antisera will be produced to both the crude and purified binding species and both these sera and the purified binding species will be tested in both clonal and primary mixed nerve-muscle cultures in an effort to block specific nerve muscle trophic interaction in vitro.